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Full Idea
Were it not for the connection to intuition, geometry would have no objective validity whatever, but be mere play by the imagination or the understanding.
Gist of Idea
Geometry would just be an idle game without its connection to our intuition
Source
Immanuel Kant (Critique of Pure Reason [1781], B298/A239), quoted by Stewart Shapiro - Thinking About Mathematics 4.2
Book Ref
Shapiro,Stewart: 'Thinking About Mathematics' [OUP 2000], p.90
A Reaction
If we pursue the idealist reading of Kant (in which the noumenon is hopelessly inapprehensible), then mathematics still has not real application, despite connection to intuition. However, Kant would have been an intuitionist, and not a formalist.